Immunochemical analysis of intact M protein secreted from cell wall-less streptococci.
M protein is a major virulence factor of group A streptococci, which provides these organisms with protection against phagocytosis in the absence of specific antibody. To gain insight into the nature of the native M-protein molecule, type 12 M protein was isolated and purified from the extracellular supernatants of a group A streptococcal L form and stabilized protoplasts. The intact purified M protein from both sources had a molecular weight of 58,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This is in contrast to the 32,0000-dalton molecule isolated from the parent type 12 organism by using a nonionic detergent. The purified secretory M protein removed opsonic antibodies from type 12 rabbit immune serum, as demonstrated by a bactericidal assay. Therefore, it appears that either previous nondestructive methods of M-protein isolation have not removed intact M protein from cell walls or part of the molecule is fragmented during its association with cell walls.
D000818:Animals; D001426:Bacterial Proteins / Q000276:immunology / Q000378:metabolism*; D002473:Cell Wall / Q000382:microbiology; D004591:Electrophoresis, Polyacrylamide Gel; D005779:Immunodiffusion; D007740:L Forms; D010587:Phagocytosis; D011523:Protoplasts / Q000378:metabolism; D011817:Rabbits; D013297:Streptococcus pyogenes / Q000276:immunology*
D001426:Bacterial Proteins